In mining machines, especially coal-cutting machines and conveyors and generally wherever masses of mineral matter must be handled efficiently, the cutting members may be mounted upon chains or conveyor flights, may be carried by chains which pass around and are engaged by a sprocket wheel or a number of sprocket wheels.
Such sprocket wheels generally have a hub portion from which a number of angularly equispaced teeth project with pockets being formed between the teeth.
Sprocket wheels of this type are increasingly required to withstand greater loading because of the increasing efforts to develop the productivity of mines, etc. As the loads, to which the conveyor system is subjected, increase, the chains must be made larger and efforts must be made to enable the sprocket wheels to withstand the additional loading. This has been achieved in the past by doubling or otherwise increasing the number of wheels and chains on a common shaft or axis, making larger and more massive wheels, etc.
The multiplication of wheels and chains greatly increases the repair and maintenance costs and complicates maintenance procedure so taht downtime is increased.
Another alternative which has been proposed is to fabricate the sprocket wheel from expensive high-alloy steels such as 42Cr Mo4 or 37Mn Si5. Such wheels were fabricated by casting and the life of the wheel could be increased by machining the sprockets in material-removal techniques and by surface hardening the wheels. While the life of a sprocket wheel could be increased by the expedients described because of the reduced wear, the disadvantages were not entirely eliminated because the sprocket wheels tended to break. Indeed, especially the surface-hardened sprocket wheels were subjected to breakage and such breakage interfered with the high and continuous rates of recovery of coal which were especially necessary for continuous power plant operations and continuous milling processes to prepare the coal for combustion, all of which depend upon the continuous availability of the coal.